1. Technical Field
The present application relates to a method for updating a digital road map which represents a road system and in which road segments having segment lengths are stored.
2. Background Art
Digital road maps are required in road toll systems, for example, which are based on a map matching process. In such systems, vehicles carry onboard units (OBUs), which continually generate readings of their own positions, so as to compare these to the digital road map and determine the respective nearest road segments as having been driven. The segment lengths of the driven road segments are then added so as to calculate and thereafter impose tolls on the length of the path traveled by the vehicle.
So as to generate the position readings, an OBU determines its own location, for example in a global navigation satellite system (GNSS) or in a public land mobile network using several stationary transceivers. Depending on the configuration, the OBU either transmits the position readings to a central unit of the road toll system, where the map matching is carried out (“thin-client OBU”), or the digital road map is stored directly in the OBU, which carries out the map matching itself (“thick-client OBU”).
Map matching methods have the drawback that the accuracy of the path length determination is limited by the segment resolution of the digital road map. The lengths of the paths in fact traveled by a vehicle frequently deviate from the lengths of the digitally modeled road segments: for example in the region of curves, intersections or traffic circles, the path actually driven is dependent on the driving direction of the vehicle, while the segment lengths of the digital road map are generally modeled independently thereof. Construction sites, temporary detours and the like also cause errors in the path lengths of the vehicles determined by way of map matching.